1. Field
Example embodiments relate to methods of growing a nitride semiconductor layer.
2. Description of the Related Art
Electronic industries using nitride semiconductors have drawn attention as fields suitable for development and growth of green industries. In particular, GaN, a nitride semiconductor, is widely used to manufacture a blue light-emitting diode from among red, green, and blue light-emitting diodes, which are essential elements of high power electronic component devices including a light-emitting diode (LED). A blue LED using GaN is more desirable in terms of brightness, lifespan, and internal quantum efficiency to conventional blue light-emitting devices using a semiconductor material, for example, zinc selenide (ZnSe), due to improved physical and chemical characteristics of GaN.
Also, because GaN has a direct transition band gap structure and the band gap is adjustable in a range from about 1.9 eV to about 6.2 eV by using an indium (In) or aluminum (Al) alloy, GaN is useful in optical devices. Also, because GaN has a higher breakdown voltage and is stable at higher temperatures, GaN is useful in various fields, e.g., a relatively high power device and a relatively high temperature electronic device. For example, GaN may be applied to a relatively large electric board using a full color display, a traffic light, a light source of an optical recording medium, and a relatively high power transistor of a vehicle engine.
Because an LED using a GaN substrate has less defects, has identical refractive indices in the GaN substrate and a device layer, and has a thermal conductivity that is about 4 times higher than that of sapphire, GaN is an essential element for manufacturing a relatively high power LED.
Because gallium nitride (GaN) from among nitride semiconductors has a band gap energy of about 3.39 eV and is a relatively wide band gap semiconductor material with a direct transition band gap, GaN is useful to manufacture a light-emitting device for emitting light having a relatively short wavelength.
Because growth of a single crystal of GaN in a liquid phase requires a relatively high temperature equal to or higher than about 1500° C. and a nitrogen atmosphere of about 20,000 atm due to a relatively high nitrogen vapor pressure at a melting point, mass producing the single crystal of GaN may be difficult. Also, because a size of the single crystal of GaN that may be currently used is about 100 mm2, using the single crystal of GaN to manufacture a device may be difficult.
Accordingly, a GaN thin film is grown on a heterogeneous substrate by using a vapor deposition method, e.g., metal organic chemical vapor deposition (MOCVD) or hydride vapor phase epitaxy (HVPE).
However, when GaN grown on a silicon substrate directly contacts silicon, the silicon may diffuse into the GaN, a surface of the silicon substrate may be etched to cause meltback, and cracks may occur due to a tensile stress when the GaN is grown on the silicon substrate due to a difference in a thermal expansion coefficient and a lattice constant between the silicon and the GaN. To solve this problem, although a method of growing GaN on a silicon substrate by using a graded buffer layer is used, the method may include growing a GaN thin film but has a limitation in growing a thick GaN layer.